Sputtering processes are employed to deposit thin films onto substrates to manufacture any of a variety of devices. Sputtering processes typically involve bombarding a solid sputtering target with energized particles to eject atoms from the target. In recent years, there has been a growing need for large area sputtering targets. This is especially so for certain applications in which large sized products are made. For example, flat panel displays often require the deposition of uniform thin films onto a substrate. The demand for larger displays, such as for televisions, continues to strain materials producers to develop alternative approaches to the efficient supply of such materials.
In one specific application, according to U.S. Pat. No. 7,336,324 (Kim et al), the deposition of a molybdenum-titanium barrier layer onto a substrate has been employed for the manufacture of a liquid crystal display device. Such application intensifies the need for large display devices capable of delivering such materials, particularly targets that contain both molybdenum and titanium.
In the manufacture of large area sputtering targets it is often deemed critical and imperative that the target exhibit uniformity in composition, microstructure, or a combination of both. For some device manufacturers that rely upon the targets to manufacture devices, the slightest imperfections are perceived as a potential quality control risk. By way of example, one concern for manufacturers is the potential formation of particles (e.g., atomic clusters or aggregates having an atomic composition different than the atomic composition of other regions of the film) during device manufacture. U.S. Pat. No. 6,755,948 (Fukuyo et al) discusses the potential effects of particles in the context of titanium targets.
Activities in the sputtering target field are illustrated by reference to a number of patent filings. By way of illustration, U.S. Patent Application No. 20070089984 describes the formation of a large area sputtering target by the use of a powder between cold-isostatically pressed blocks of a mixture of molybdenum and titanium powders. The use of such powder generally results in the formation of a conspicuous joint line between adjoining blocks that may appear as a band. Even if such joint line does not actually adversely affect performance, its conspicuous nature is a potential concern for device manufacturers. For instance, some manufacturers have the perception that the joint line may contribute to the formation of undesired particles during sputtering; if generated, there is a belief that such particles potentially might affect performance of resulting devices.
U.S. Pat. No. 4,594,219 (Hostatter et al) addresses side-by-side consolidation of preforms to form complex or compound shaped articles (e.g., connecting rods and hand wrenches). Consolidation (e.g., by hot isostatic pressing) of molybdenum and/or titanium powder containing performs is not described. Moreover, particular processing steps to achieve successful results in the consolidation of molybdenum and/or titanium powder containing performs is also not described.
U.S. Patent Application No. 20050191202 (Iwasaki et al) discloses a molybdenum sputtering target (in which an example is provided of a 70.0 at % Mo-30.0 at/% Ti material). The application discloses a requirement for use of relatively high temperatures and pressures, stating at paragraph 40 that if a pressure below 100 MPa and a temperature below 1000° C. is used, “it is hard to produce the sintered body having a relative density of not less than 98%”. The application describes a process by which a relatively large size body is consolidated from secondary powders and then the sintered body is cut into separate targets. One example illustrates a further hot plastic working step.
U.S. Patent Application Publication 20050189401 (Butzer) discloses a method of making a large Mo billet or bar for a sputtering target wherein two or more bodies comprising Mo are placed adjacent one another (e.g. stacked one on the other) with Mo powder metal present at gaps or joints between the adjacent bodies. The adjacent bodies are hot isostatically pressed to form a diffusion bond at each of the metal-to-Mo powder layer-to-metal joint between adjacent bodies to form a billet or bar that can be machined or otherwise formed to provide a large sputtering target. This patent publication appears to disclose bonding of major side surfaces, not edge-to-edge bonding of plates.
U.S. Patent Application No 20080216602 (Zimmerman et al) describes another method for making large area sputtering targets with a molybdenum-titanium composition, which includes a cold spray deposition step for joining a plurality of targets at an interface. Though acknowledging certain electron beam welding and hot isostatic pressing processes to join targets, in paragraphs 165-166 (referring to FIGS. 17 and 18), the patent application indicates that electron beam welding results in porosity, and the hot isostatic pressing results in a brittle alloy phase.
U.S. Patent Application No. 20070251820 (Nitta et al) describes an example of another approach to the manufacture of a molybdenum-titanium sputtering target. In this publication, diffusion joining (at a temperature of at least 1000° C.) of two or more previously sintered or melted sputter targets along at least one side. The use of a Mo—Ti powder in the joint is described.
U.S. Patent Application No. 20070289864 (Zhifei et al) identifies a need in large area sputtering targets to fill gaps between multiple target sections carried on a common backing plate. The patent illustrates the material deposition processes between adjoining target portions. Interestingly, the patent recognizes that the manufacture of large molybdenum plate targets poses difficulties, and the need for efficient manufacturing.
In view of the above, there remains a need in the art for alternative sputtering targets (especially large size targets, such as targets exceeding about 0.5 meters, about 1 meter, or even about 2 meters for its largest dimension), and approaches to their manufacture that meet one or any combination of the needs for general uniformity of composition, general uniformity of microstructure, insubstantial likelihood of particle formation, relatively thin and virtually invisible joint line between target components, or relatively high strength (e.g., relatively high transverse rupture strength).